With advancements of the display technology, an Organic Light Emitting Diode (OLED) is one hot spot of a research field for current panel displays; more and more Active Matrix Organic Light Emitting Diode (AMOLED) display panels have come into the market, and as compared with a traditional Thin Film Transistor Liquid Crystal Displays (TFT LCDs), the AMOLEDs are of a faster response speed, a higher contrast as well as a wider viewing angle. The AMOLED is an autonomous light emitting device, and may realize a broad viewing angle display and may realize a panel display such as an ultra-thin display, a flexible display, etc., without an assistance of a backlight; the AMOLED is capable of emitting light because it is driven by a current generated by a drive transistor in a pixel circuit when the drive transistor is in a saturation state.
Generally, as shown in FIG. 1, an existing pixel circuit consists mainly of seven transistors of M1-M7 and one capacitor C, wherein the transistor M3 is a drive transistor; when the AMOLED display panel is started up to display a first frame, prior to the pixel circuit being charged, a power supply signal VDD loaded onto the pixel circuit is generally a ground level signal, i.e., 0V, then a gate voltage of the drive transistor M3 in the pixel circuit is 0V−Vth (Vth is a threshold voltage of the drive transistor); and during a light emitting stage, the power supply signal loaded onto the pixel circuit becomes a high voltage (for example 4.5V), and a voltage difference Vgd between a gate and a drain of the drive transistor M3 (the voltage difference between the Gate-Drain, which determines turning-on or turning off the TFT) becomes larger, and a voltage signal for driving the OLED to emit light becomes abnormal, therefore a drive current for driving the OLED to emit light which is output by the drive transistor M3 also becomes an abnormally large current; then even if a normal drive current is output by the pixel circuit for a next frame, a problem of screen flicker may occur in the first frame in the startup screen due to the aforementioned abnormal drive occurring in the screen of the first frame.
In addition, before a low level signal is loaded onto the pixel circuit, since an output terminal for outputting a low level signal in a power supply signal chip is in a floating state, and an output terminal for outputting a high level signal to the pixel circuit in power supply signal chip is on, and since after the transistors M3 and M6 are both turned on, the low level signal terminal VSS is at a positive potential; and when the low level signal output terminal of the power supply signal chip is on, since the low level signal terminal VSS of the pixel circuit is at the positive potential, there are difficulties for the low level signal terminal VSS of this pixel circuit to receive a signal, thus the power supply signal chip for providing the power supply signal may be damaged or broken; in this case, a self-protection device of the power source chip may perform a protection function and cut off the power source, which may cause the abnormal displaying of the display panel screen.
Accordingly, the technical problems needed to be solved by those skilled in the art are as follows: how to overcome the problem of screen flicker due to the abnormal drive current output by the pixel circuit when the display panel is started up and the first frame is displayed on a screen; and how to overcome the problem of the abnormal displaying of the display panel due to the self-protection function of a power supply signal chip triggered by the difficulty for the low level signal terminal of the pixel circuit receiving a positive potential and a negative potential.